How does the fan engage?

I'm planning a roadtrip to the Netherlands soon from Germany, and this'll be in the summer. Naturally given the heat, I wanna ensure my car has no cooling issues on the trip, especially if I hit any construction sites with heavy traffic.

One of my concerns is that my fan isn't engaging. I never checked if it's engaged when the car is running, but, is the fan gel-based or is it based on a temp sensor?